Fix timer table set failed

[sy-records]

Fix #648

The maximum number of rows a table can store is positively related to $size, but not exactly the same, e.g. $size is 1024 and the actual number of rows that can be stored is less than 1024.

So add a configuration item and let the user go and configure it according to the actual situation.

This code can be used to reproduce the problem.

use Swoole\Table;

$table = new Table(1024);
$table->column('worker_pid', Table::TYPE_INT);
$table->column('time', Table::TYPE_INT);
$table->column('fd', Table::TYPE_INT);

$table->create();

foreach (range(1, 1050) as $i) {
    $table->set($i, [
        'worker_pid' => $i,
        'time' => time(),
        'fd' => $i,
    ]);
}

var_dump($table->stats(), $table->getSize());

[driesvints]

Thanks @sy-records